1. Technical Field
The invention includes embodiments that relate to a composition for use as a cathode material in an energy storage device. The invention includes embodiments that relate to the energy storage device.
2. Discussion of Art
Work has been done on rechargeable batteries using sodium as the negative electrode in a battery cell. Sodium has a standard reduction potential of −2.71 volts. Sodium is relatively low weight, non-toxic, abundant, and economically desirable in the form of sodium chloride. The sodium anode may be used in liquid form, and the melting point of sodium is 98 degrees Celsius. An ion conducting solid electrolyte (separator) separates the liquid sodium anode from a positive electrode (cathode).
A second, molten electrolyte transports ions to and from the separator on the cathode side. The melting point of the molten electrolyte, along with the temperature-dependent, sodium-ion conductivity of the solid electrolyte, determines the minimum operating temperature of the battery. The cathode should include a material that is soluble in the molten electrolyte and is compatibility with the solid electrolyte in the charged (oxidized) state. Low solubility of the oxidized cathode material in the molten electrolyte can lead to passivation of the remaining uncharged (reduced) electrode surface and fouling of the pores.
It may be desirable to have an electrochemical cell that has different chemistry than those electrochemical cells that are currently available. It may be desirable to have an energy storage device that differs from those devices that are currently available.